Probehead for nmr spectometer

ABSTRACT

The invention relates to the probehead of nuclear magnetic resonance spectrometer comprising a frame, a radio frequency coil attached thereto and a rotor located inside the coil containing the examined sample, supported by bearings and provided with turbines at both ends, a source of compressed gas, an executive unit and a control unit. The innovative step involves using different turbines that make the rotor rotate in the same or in opposite directions and providing the executive unit with at least two compressed gas channels for rotor velocity control for each turbine, whereas the coil is connected to the inner surface of the frame with at least two, preferably four sheets of thin non-conductive and non-magnetic material. The rotation velocity of the probehead rotor can be controlled and the rotation direction reversed thereby obtaining additional information on the examined sample during the measuring process.

The invention relates to radiospectroscopy and deals in particular withprobehead for nuclear magnetic resonance (NMR) measurement.

NMR is a method of radiospectroscopy for study of structural and dynamicproperties of the matter. In order to narrow detected spectral lines andimprove resolution, a fast mechanical rotation of the sample undercertain angle with respect of the magnetic field direction is used. Aknown patent of E. Lippmaa et.al. U.S. Pat. No. 4,254,373, Int Cl³ G01R33/08, 1981, describes a probehead, containing a rotor with the studiedsample. A radio-frequency NMR coil is wound around the rotor, leaning onbearings and equipped with turbines, executive unit and control unit. Ashortcoming of the known probehead is unvariable rotor speed, limitingthe content of obtained information about the sample in certain cases.

The goal of the invention is to obtain information about the sampleunder conditions of fast rotor velocity change and inversion of therotation direction.

The task is solved in such a manner, that in the NMR probehead,containing a sample in the rotor, surrounded by radio-frequency NMRcoil, and supported by bearings and provided with the turbines at bothends, source of the compressed gas, execution unit and control unit,different turbines make the rotor rotate in the same or in oppositedirections and executive unit comprises at least two compressed gaschannel for rotor velocity control for each turbine. Sufficiently fastalteration of the rotor velocity and direction of rotation are possibleby means of several turbines.

In the preferred embodiment there are two turbines at each end of therotor and the executive unit has been provided with four velocitycontrol compressed gas channels. Thus at each end of the rotor there's aturbine that makes the rotor rotate in one direction and another turbinethat makes it rotate in the opposite direction. The increased number ofturbines allows to increase the start acceleration of rotation byapplying higher momentum to the rotor.

It is also preferred that the diameter of the cylindrical turbines isless than the diameter of the rotor when achieving maximum velocity in aprovided direction of rotation is the relevant parameter. E.g. when thediameter of the cylindrical turbine is decreased two times, then at thesame linear velocity the angular velocity doubles.

In order to achieve higher velocity and to speed up reversing therotor's direction of rotation the dimensions of the turbines have beenbrought down to the minimum. But the relatively small volume of therotor and thus the examined example in comparison with the area of theexamined sample causes a distortion of the measured signal due to theinhomogeneity of the magnetic field during passage from one environmentto another when the magnetic susceptibility of the environments isdifferent. Therefore it is preferable either to unify the susceptibilityor to minimize the mass of substance with different receptiveness aroundthe rotor.

In order to decrease signal distortion the coil is preferably connectedto the inner surface of the frame with at least two, preferably foursufficiently strong thin non-conductive and non-magnetic sheets that arepreferably positioned radially. The most suitable material is ceramics.In order to combine the coil and the ceramic sheet the coil end of theceramic sheet is provided with grooves that house coil sections.

The length and thickness ratio of the ceramic sheet is preferably 200:1to 50:1. A higher ratio may cause the sheet to break, a lower ratio maycause the homogeneity of the magnetic field to be compromised.

Signal distortion by magnetic field inhomogenity is reduced byminimizing bulk volume of the coil and supporting construction. The coilis supported by very thin sheets or stripes of strong, non-conductiveand non-magnetic material (typically technical ceramic). The rotorvelocity of the probehead can be modified and direction of the rotationchanged, all this enables to obtain additional information about theinvestigated sample. The information is detected in a form ofelectromagnetic waves, picked up by a special coil. The coil is locatedas close as possible around the rotor, and may need mechanical supportfor exact and stable positioning. The coil and support are carefullyselected to avoid disturbance of the magnetic field homogeneity. Novelfeature of present invention is also special support construction,designed to minimize bulk susceptibility changes around the sample. Thesupport comprises two or more thin sheets of sufficiently strongmaterial, fixing coil by either tangential or radial mechanical contact.Sufficiently high acceleration rates of the rotor can only be achievedfor rotors of no more than few mm in diameter. Relatively small volumeof the sample makes overall signal sensitive for construction featuresof details around the sample. Therefore, coil support presents a logicalpart of the whole probehead.

FIG. 1 presents a principal layout of four turbine probehead.

FIG. 2 presents construction for signal pickup coil support, based onradially arranged ceramic sheets.

FIG. 3 presents perpendicular view A-A from FIG. 2.

NMR probehead contains investigated sample, located in the rotor 1. Therotor 1 leans on bearings 2 and is equipped with turbines. The turbines3 and 6 generate motion, which may be reversed compared to turbines 4and 5. In principle, only two turbines are required for realisingphysical idea of the experiment. Larger number of turbines may berequired to achieve sufficiently high acceleration rate of the rotor, bydelivering more momentum to the rotor. The source of high-pressure gas 7is connected with turbines via execution unit 8, which is operated by acontrol unit 9. Coil 10 is supported by very thin ceramic sheets 11,connected to the frame 12 e.g. by glued joint. Sufficiently highacceleration rates of the rotor can only be achieved for rotors of nomore than few mm in diameter. Diameter of rotor in realized embodimentis 1.8 mm and diameter of working surface of turbines is 1.6 mm.

Operation principle of the NMR probehead is following. The rotor 1 isfilled with a measured sample. A suitable combination of the turbines isselected to activate motion. Change of the rotor speed or its reversalis accomplished by execution unit 8. The execution unit 8 compriseseither valves or switches, located either in the probehead orexternally, and switched typically by electromagnets. The purpose beingregulation of the pressure and amount of the compressed gas, flowingfrom the reservoir 7 to the turbines 3-6, as determined by signal fromthe control unit 9. For a rapid acceleration of the rotor, executionunit will increase gas pressure at forward turbines. Deceleration, stopor reversal of the rotor motion pressure is increased atcounter-directed turbines, reducing simultaneously gas flow to forwardturbines.

Total number of turbines can be two (one for each direction, or bothsame direction, one of which to provide acceleration), but in this casethe efficiency of the rotor acceleration is correspondingly reduced.

Described probehead is applied for modification of dipolar interactionbetween atoms in studied sample. This process is able to carry spectralfrequency, characterizing atom A, to atom B and further to atom C,proving spatial proximity of atoms A and C. Novel feature is usingauxiliary, messenger atom B for information transport. The probeheadenables also significantly more extended distance of the informationtransport.

Very important practical application of this probehead is a possibilityto determine sequence of amino acids in peptides and proteins. Atoms Aand B are alfa-carbons of the neighboring amino acids, auxiliarymessenger atom is carbonyl carbon in between.

1. A probehead for measuring nuclear magnetic resonance that iscomprised of a frame, a radio frequency coil attached thereto and arotor located inside the coil containing the examined sample, supportedby bearings and provided with turbines at both ends, a source ofcompressed gas, an executive unit and a control unit, characterized inthat different turbines make the rotor rotate in the same or in oppositedirections and the executive unit is provided at least two separatecompressed gas channels for rotor velocity control for each turbine. 2.A probehead as claimed in claim 1 characterized in that at both ends ofthe rotor there are two turbines respectively to provide rotation inopposite directions and the executive unit has been provided with fourcompressed gas channels for rotor velocity control.
 3. A probehead asclaimed in claim 1 characterized in that the turbines are cylindricaland the diameter of their work area is less than the diameter of therotor.
 4. A probehead as claimed in claim 1 characterized in that thecoil is connected to the inner surface of the frame with at least two,preferably four sheets of thin non-conductive and non-magnetic material.5. A probehead as claimed in claim 4 characterized in that the sheetsare made of ceramic material.
 6. A probehead as claimed in claim 4characterized in that the coil ends of the sheets comprise grooves forhousing coil sections.
 7. A probehead as claimed in claim 4characterized in that the ratio of the length and thickness of thesheets is 200:1 to 50:1.